3G科普之W-CDMA

W-CDMA
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Wideband Code Division Multiple Access 宽带CDMA) 是一种3G蜂窝网络。WCDMA UMTS使用的部分协议与2G GSM 标准一致。
具体一点来说，W-CDMA是一种利用码分多址复用(或者CDMA 通用 复用技术，不是指CDMA标准)方法的宽带扩频3G移动通信空中接口。

历史概要

历史上，欧洲电信标准委员会 (ETSI) 在 GSM 之后就开始研究其 3G 标准，其中有几种备选方案是基于直接序列扩频CDMA的，而日本的第三代研究也是使用宽带CDMA技术的，其后，以二者为主导进行融合，在3GPP组织中发展成了第三代移动通信系统UMTS，并提交给国际电信联盟(ITU)。
国际电信联盟最终接受WCDMA作为IMT-2000 3G标准的一部分。

误解

名字跟CDMA很相近，同时WCDMA跟CDMA关系也很微妙。两者都基于码分多址技术，都使用了美国高通（Qualcomm）的部分专利技术。一般认为WCDMA的提出是部分厂商为了绕开专利陷阱而开发的，其方案已经尽可能地避开高通专利。

在移动电话领域，术语 CDMA 可以代指码分多址扩频复用技术，也可以指美国高通（Qualcomm）开发的包括IS-95/CDMA1X和CDMA2000(IS-2000)的CDMA标准族。

在Qualcomm为IS-95协议使用它之前，CDMA复用技术已经存在了很长时间。然而，由于采用CDMA复用方法是IS-95协议区别于当时的GSM（采用TDMA）等其它协议的主要特征，现在通常将该协议也称为CDMA。

WCDMA 也使用CDMA的复用技术而且它跟Qualcomm的标准也很相似。但是WCDMA不仅仅是复用标准。它是一个详细的定义移动电话怎样跟基站通讯，信号怎样调制，数据帧怎么构建等的完整的规范集。

总之:

* 术语CDMA在移动通讯领域通常特指Qualcomm开发的CDMA标准族。它们定义了一组移动通讯协议。
* CDMA作为复用技术，既用于W-CDMA空中接口协议，也用于Qualcomm的CDMA协议。
* W-CDMA专指在IMT-2000中定义的移动电话协议。
* W-CDMA协议与Qualcomm开发的CDMA无关。
* CDMA标准族(IS-95/cdmaOne和CDMA2000)不兼容W-CDMA标准族。

当前状况

2001年，日本NTT DoCoMo公司的FOMA是世界上第一个商业运营W-CDMA服务。 FOMA不兼容UMTS。

J-Phone 日本电话(现沃达丰)已经继推出基于W-CDMA服务后，声称“沃达丰全球标准”兼容UMTS (尽管2004年时还有争议)。

2003年初，和记黄埔 逐步在全球运营他们的UMTS网络(简称3，参见en:3)。

大多数欧洲GSM运营商计划未来某个时间推出UMTS服务，尽管有几个已经把此服务提到日程上来，有一些甚至从2003年底就开始运营UMTS网络。

沃达丰于2004年2月在欧洲多个UMTS网络投入运行。沃达丰还打算在其他国家（包括澳大利亚及新西兰）建设UMTS网络。

AT&T 无线 (现属于Cingular Wireless) 在一些城市开通了UMTS。尽管因为公司兼并使得网络建设进度被延迟，但Cingular已宣布计划在2005年与HSDPA一起部署W-CDMA。

TeliaSonera于2004年10月13日开始在芬兰提供384kbps速率的W-CDMA服务。服务只是在主要城市可用。通讯费率大约2美元每兆字节。

产品认证

* GCF (Global Certification Forum)：现时是世界主要的2G及3G认证机构。
* PTCRB: 在北美为GSM移动设备（ME）类型认证提供框架。

技术

W-CDMA可以使用非成对或者成对频段，虽然所有当前W-CDMA设备（例如FOMA and UMTS）使用两个5MHz频段，一个用于上行一个用于下行。更多信息请参看扩频。

与其他标准比较

* 最初CDMA2000计划使用多个1.25MHz载波，但后来放弃了，而WCDMA则使用单一5MHz带宽载波。
* 在ITU的IMT-2000标准中，WCDMA被看作CDMA直接序列扩频，而CDMA2000被称作"多载波CDMA"。
* WCDMA 标准族(例如FOMA、UMTS)与CDMA标准族(例如IS-95和CDMA2000)不一致。


W-CDMA
From Wikipedia, the free encyclopedia

W-CDMA (Wideband Code Division Multiple Access) is a type of 3G cellular network. W-CDMA is the technology behind the 3G UMTS standard and is allied with the 2G GSM standard with the International Telecommunication Union - ITU.

More technically, W-CDMA is a wideband spread-spectrum 3G mobile telecommunication air interface that utilizes code division multiple access (or CDMA the general multiplexing scheme, not to be confused with CDMA the US standard).

History

W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network FOMA. Later NTT DoCoMo submitted the specification to the International Telecommunication Union (ITU) as a candidate for the international 3G standard known as IMT-2000. The ITU eventually accepted W-CDMA as part of the IMT-2000 family of 3G standards. Later, W-CDMA was selected as the air interface for UMTS, the 3G data part of GSM. Attempts were made to unify W-CDMA (3GPP) and CDMA-1X (3GPP2) standards in order to provide a single worldwide standard. However, divergent requirements resulted in the two incompatible standards being retained.

Features

Only key features are cited below.

* Supports two basic modes of duplex: FDD (frequency division duplex) and TDD (time division duplex) modes
* Employs coherent detection on uplink and downlink based on the use of pilot symbols
* Inter-cell asynchronous operation
* Variable mission: on a 10 ms frame basis
* Multicode transmission
* Adaptive power control based on SIR
* Multiuser detection and smart antennas can be used to increase capacity and coverage
* Multiple types of handoffs between different cells including soft handoff, softer handoff and hard handoff

Misconceptions

W-CDMA is based on the Direct Spread CDMA technique. Code Division Multiple Access has been developed by a number of companies, and in the US this is dominated by Qualcomm. However, the ITU standard is not a Qualcomm implementation, but one where Qualcomm has been invited to participate. Other standards, such as TD-SDMA/TD-CDMA, have been developed by Siemens and Chinese companies independent of both the ITU and Qualcomm and bears no relationship with the US technology other than the name others have assigned to it.

In the mobile phone world, the term CDMA can refer to either the Code Division Multiple Access spread spectrum multiplexing technique, or the CDMA family of standards developed by Qualcomm, including cdmaOne (IS-95) and CDMA2000 (IS-2000 and IS-856).

The CDMA multiplexing technique existed long before Qualcomm used it for its IS-95 protocol. However, this protocol is now widely referred to as "CDMA" for its principal characteristic of using the CDMA multiplexing scheme to share multiple connections divided by different codes (PN sequences) over the same spectrum channel, as opposed to other spectrum division schemes

Qualcomm was able to introduce the first mobile protocol relying upon the CDMA multiplexing technique, associating the multiplexing technique with the name of the protocol.

W-CDMA is used in 3G as a political compromise made by the more advanced non-US companies to allow the US to participate in the rollout of 3G services. Since it now is part of the International Telecommunication Union's standards it is part of a larger suite of standards. W-CDMA is a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.

In summary:

* The term CDMA in the mobile world typically refers to the CDMA family of standards developed by Qualcomm. They are protocols, sets of defined specifications of mobile communications
* CDMA (the multiplexing technique) is used as the principle of the W-CDMA air interface protocol, as well as Qualcomm's CDMA protocols
* W-CDMA strictly refers to a mobile phone protocol with detailed specifications, as defined in IMT-2000
* The W-CDMA protocol was developed independently of the CDMA protocol developed by Qualcomm.
* The CDMA family of standards (including cdmaOne and CDMA2000) are not compatible with the W-CDMA family of standards that are based on ITU standards.

Implementations

The world's first commercial W-CDMA service, FOMA, was launched by NTT DoCoMo in Japan in 2001. FOMA is compatible with standard UMTS. But the effort for migrating the FOMA specifications to UMTS are indicated by Japan.

J-Phone Japan (now Vodafone) soon followed by launching their own W-CDMA based service, originally branded "Vodafone Global Standard" and claiming UMTS compatibility. The name of the service was changed to "Vodafone 3G" in December 2004.

Beginning in 2003, Hutchison Whampoa gradually launched their upstart UMTS networks.

Most countries have since the ITU approved of the 3G mobile service either "auctioned" the radio frequencies to the company willing to pay the most, or conducted a "beauty contest" - asking the various companies to present what they intend to commit to if awarded the licenses. This strategy has been criticised for aiming to drain the cash of operators to the brink of bankruptcy in order to honour their bids or proposals. Most of them have a time constraint for the rollout of the service - where a certain "coverage" must be achieved within a given date or the license will be revoked.

Vodafone launched several UMTS networks in Europe in February 2004. MobileOne of Singapore commercially launched its 3G (W-CDMA) services in February 2005. New Zealand in August 2005 and Australia in October 2005.

AT&T Wireless (now a part of Cingular Wireless) has deployed UMTS in several cities. Though advancements in its network deployment have been delayed due to the merger with Cingular, Cingular began offering HSDPA service in December 2005.

Rogers in Canada is currently trialing HSDPA on W-CDMA at 1900MHz and plan the launch the service commercial in Q3, 2006.

TeliaSonera opened W-CDMA service in Finland October 13th 2004 with speeds up to 384 kbit/s. Availability only in main cities. Pricing is approx. 2€/MB. SK Telecom and KTF, two largest mobile phone service providers in South Korea, have each started offering W-CDMA service in December 2003. Due to poor coverage and lack of choice in handhelds, the W-CDMA service has barely made a dent in the Korean market which was dominated by CDMA2000. By October 2006 both companies are covering more than 90 cities while SK Telecom has announced that it will provide nationwide coverage for its WCDMA network in order for it to offer SBSM (Single Band Single Mode) handsets by the first half of 2007. KT Freecel will thus cut funding to its CDMA2000 network development to the minimum.

In Norway, Telenor introduced W-CDMA in major cities by the end of 2004, while their competitor, NetCom, followed suit a few months later. Both operators have 98 % national coverage on EDGE, but Telenor has parallel WLAN roaming networks on GSM, where the UMTS service is competing with this. For this reason Telenor is dropping support of their WLAN service in Austria (2006).

Maxis Communications and Celcom, two mobile phone service providers in Malaysia, started offering W-CDMA services in 2005.

In Sweden, Telia introduced W-CDMA March 2004.

Technology

W-CDMA may use unpaired or paired spectrum, though the current implementations of W-CDMA (i.e. FOMA and UMTS) all use a pair of 5MHz spectrum, one for uplink and one for downlink. See Spread spectrum for more information. FOMA uses sixteen slots per radio frame, where as UMTS uses 15 slots per radio frame.